The present invention relates to a device and method for measuring the level of an oxidant or antioxidant analyte in a fluid sample. The device comprises a disposable electrochemical cell containing a reagent capable of directly undergoing a redox reaction with the analyte.
An oxidation reaction, broadly defined, involves the transfer of one or more electrons from one molecule or atom (the reducing agent or reductant) to another (the oxidizing agent or oxidant). Oxidation reactions occur in a broad range of systems, e.g., food products, living organisms, and drinking water, and may be detrimental or beneficial. Food products exposed to oxygen may undergo oxidative degradation, resulting in the generation of undesirable flavors and odors, the destruction of fat-soluble vitamins and essential fatty acids, and the production of toxic degradation products. Beneficial oxidation reactions in food products include those between natural or synthetic antioxidants and oxidants, whereby the oxidant is prevented from participating in a detrimental oxidation reaction.
Thus, it is desirable to be able to measure oxidant or antioxidant levels in liquid samples in many fields. For example, it is desirable in terms of manufacturing quality control as well as health monitoring to measure the level of preservatives such as sulfur dioxide in wine or food, the level of ascorbic acid in fruit, vegetables, beverages, and biological fluids, and the level of chlorine or peroxides in water. Most conveniently, these tests are fast and easy to use and be amenable to field as well as laboratory use.
Existing methods for measuring these components require either expensive laboratory apparatus or skilled operators in order for the method to be used successfully. For example, a sensor for detecting antioxidant agents in oil is disclosed in U.S. Pat. No. 5,518,590. However, this sensor is not designed for single, disposable use and does not use a redox agent. It is therefore desirable to have a sensor designed for single, disposable use that can detect oxidant or antioxidant levels in fluid samples through the use of a redox reagent.
The present invention provides a device and method for measuring oxidant and antioxidant analytes with a disposable sensing element, suitable for a single use, that can be combined with a meter to give a robust, fast, and easy to use test that is amenable to field as well as laboratory use. In particular, the invention relates to the use of an electrochemical sensor that utilizes a redox agent that reacts with the analyte of interest to produce an electrochemically detectable signal.
In one embodiment of the present invention, a device for detecting a presence or an absence of a redox reactive analyte in an aqueous sample is provided, the device including an electrochemical cell having a sensing chamber, a first electrode, a second electrode, an aperture for admitting the sample into the sensing chamber, and a reagent contained within the sensing chamber, wherein the electrochemical cell is designed to be disposed of after use in a single experiment, and wherein the reagent is capable of undergoing a redox reaction directly with the analyte to generate an electrical signal indicative of the presence or absence of the analyte.
In one aspect of this embodiment, the first electrode is a sensing electrode that may consist of platinum, palladium, carbon, indium oxide, tin oxide, gold, iridium, copper, steel, or mixtures thereof. The first electrode may also be silver. The first electrode may be formed by a technique such as sputtering, vapor coating, screen printing, thermal evaporation, ink jet printing, ultrasonic spraying, slot coating, gravure printing and lithography.
In another aspect of this embodiment, the second electrode is a counter electrode. The second electrode may include a metal in contact with a metal salt, for example, silver in contact with silver chloride, silver in contact with silver bromide, silver in contact with silver iodide, mercury in contact with mercurous chloride, or mercury in contact with mercurous sulfate. The second electrode may also be a reference electrode.
In another aspect of this embodiment, the electrochemical cell further includes a third electrode, such as a reference electrode. The third electrode may include a metal in contact with a metal salt, such as silver in contact with silver chloride, silver in contact with silver bromide, silver in contact with silver iodide, mercury in contact with mercurous chloride, and mercury in contact with mercurous sulfate.
In another aspect of this embodiment, the reagent is capable of oxidizing an analyte including an antioxidant. The reagent may include ferricyanide salts, dichromate salts, permanganate salts, vanadium oxides, dichlorophenolindophenol, osmium bipyridine complexes, and quinones.
In another aspect of this embodiment, the reagent is capable of reducing an analyte including an oxidant. The reagent may include iodine, triiodide salts, ferrocyanide salts, ferrocene, Cu(NH3)42+ salts, and Co(NH3)63+ salts.
In another aspect of this embodiment, the sensing chamber further includes a buffer contained within the sensing chamber. The buffer is selected from the group consisting of phosphates, carbonates, alkali metal salts of mellitic acid, and alkali metal salts of citric acid.
In another aspect of this embodiment, the device further includes a heating element. The heating element may include an electrically resistive heating element or an exothermic substance contained within the sensing chamber, such as aluminum chloride, lithium chloride, lithium bromide, lithium iodide, lithium sulfate, magnesium chloride, magnesium bromide, magnesium iodide, magnesium sulfate, and mixtures thereof.
In another aspect of this embodiment, the sensing chamber includes a support contained within the sensing chamber. Supports may include mesh, nonwoven sheet, fibrous filler, macroporous membrane, sintered powder, and combinations thereof. One or both of the reagent and buffer may be contained within or supported on the support.
In another aspect of this embodiment, the second electrode is mounted in opposing relationship a distance of less than about 500 microns from the first electrode, less than about 150 microns from the first electrode, or less than about 150 microns and greater than about 50 microns from the first electrode.
In another aspect of this embodiment, the device further includes an interface for communication with a meter. The interface may communicate a voltage or a current.
In another aspect of this embodiment, the electrochemical cell includes a thin layer electrochemical cell.
In a second embodiment of the present invention, a method for detecting a presence or an absence of a redox reactive analyte in an aqueous sample is provided which includes providing a device for detecting the presence or absence of an analyte in an aqueous sample, the device including an electrochemical cell having a sensing chamber, a first electrode, a second electrode, an aperture for admitting the sample into the sensing chamber, and a reagent contained within the sensing chamber, wherein the electrochemical cell is designed to be disposed of after use in a single experiment, and wherein the reagent is capable of undergoing a redox reaction directly with the analyte to generate an electrical signal indicative of the presence or absence of the analyte; providing an aqueous sample;allowing the sample to flow through the aperture and into the sensing chamber, such that the sensing chamber is substantially filled; and obtaining an electrochemical measurement indicative of the presence or absence of analyte present in the sample.
In one aspect of this embodiment, the electrochemical measurement is an amperometric measurement, a potentiometric measurement, a coulometric measurement, or a quantitative measurement.
In another aspect of this embodiment, the method includes the further step of heating the sample, wherein the heating step precedes the step of obtaining the electrochemical measurement. Alternatively, the method may include the additional steps of heating the sample, wherein the heating step follows the step of obtaining an electrochemical measurement; and thereafter obtaining a second electrochemical measurement indicative of the presence or absence of a second analyte present in the sample.
In another aspect of this embodiment, the sensing chamber further includes a buffer, for example, phosphate buffer, carbonate buffer, alkali metal salt of mellitic acid, and alkali metal salt of citric acid.
In a third aspect of the present invention, a method for measuring sulfur dioxide in a sample of wine is provided, the sulfur dioxide having a free form and a bound form and being capable of undergoing a redox reaction with a reagent, the redox reaction having a reaction kinetics, wherein the method includes the steps of providing a device, the device including an electrochemical cell having a sensing chamber, a first electrode, a second electrode, an aperture for admitting the sample into the sensing chamber, and a reagent capable of undergoing a redox reaction with sulfur dioxide, wherein the electrochemical cell is designed to be disposed of after use in a single experiment; placing the sample of wine in the electrochemical cell, thereby initiating the redox reaction; and obtaining a first electrochemical measurement indicative of the level of sulfur dioxide in free form.
In one aspect of this embodiment, the method further includes the steps of heating the sample of wine for a period of time sufficient for sulfur dioxide in bound form to react with the reagent, wherein the heating step is conducted after the step of obtaining a first electrochemical measurement; and thereafter obtaining a second electrochemical measurement indicative of the level sulfur dioxide in free form and in bound form combined. Alternatively, the method may include the further steps of obtaining a second electrochemical measurement indicative of the kinetics of reaction of the sulfur dioxide in bound form with the reagent, wherein the second electrochemical measurement is obtained after the step of obtaining a first electrochemical measurement; and calculating the level of bound sulfur dioxide using the kinetics of reaction.
In a fourth aspect of the present invention, a method of manufacture of a device for detecting the presence or absence of a redox reactive analyte in an aqueous sample is provided, the device including an electrochemical cell having a sensing chamber, a first electrode, a second electrode, an aperture for admitting the sample into the sensing chamber, and a reagent contained within the sensing chamber, wherein the electrochemical cell is designed to be disposed of after use in a single experiment, and wherein the reagent is capable of undergoing a redox reaction directly with the analyte to generate an electrical signal indicative of the presence or absence of the analyte, the method including forming an aperture extending through a sheet of electrically resistive material, the aperture defining a side wall of the sensing chamber; mounting a first layer having a first electrode to a first side of the sheet and extending over the aperture, defining a first sensing chamber end wall, the first electrode facing the first side of the sheet; mounting a second layer having a second electrode to a second side of the sheet and extending over the aperture defining a second sensing chamber end wall in substantial overlying registration with the first layer, the second electrode facing the second side of the sheet, whereby the sheet and layers form a strip; forming an aperture in the strip to permit entry of a sample into the sensing chamber; and providing a reagent capable of undergoing a redox reaction directly with the analyte, wherein the reagent is contained within the sensing chamber.
In one aspect of this embodiment, the method includes the further step of providing a vent in the strip to permit escape of air displaced from the sensing chamber when sample fills the sensing chamber. Another further step includes mounting an electrically resistive heating element to the strip.
In a further aspect of this embodiment, the aperture is of a rectangular cross-section.
In a further aspect of this embodiment, at least one of the electrodes includes a noble metal, for example, palladium, platinum, and silver. At least one of the electrodes may be a sputter coated metal deposit. The electrodes may be adhered to the sheet, for example, by an adhesive such as a heat activated adhesive, pressure sensitive adhesive, heat cured adhesive, chemically cured adhesive, hot melt adhesive, or hot flow adhesive.
In a further aspect of this embodiment, the method includes further steps such as providing an exothermic substance or buffer contained within the sensing chamber; printing the reagent or buffer onto at least one wall of the sensing chamber; or providing a support such as mesh, fibrous filler, macroporous membrane, sintered powder, and combinations thereof contained within the sensing chamber. The reagent may be supported on or contained within the support.
In a further aspect of this embodiment, at least the sheet or one of the layers of the device manufactured according to the method is a polymeric material selected from the group consisting of polyester, polystyrene, polycarbonate, polyolefin, and mixtures thereof. Alternatively, at least the sheet or one of the layers is polyethylene terephthalate.
In a further aspect of this embodiment, the second electrode is mounted in opposing relationship a distance of less than about 500 microns from the first electrode; less than about 150 microns from the first electrode; or less than about 150 microns and greater than about 50 microns from the first electrode.